1. Field of the Invention
The present invention relates to a receiver apparatus and method for tracking and rejecting a Transmit (Tx) signal in a wireless communication system. More particularly, the present invention relates to an apparatus and method for rejecting a Tx signal introduced to a receiver by performing frequency tracking in a wireless communication system employing a Frequency Division Duplex (FDD) scheme.
2. Description of the Related Art
Conventionally, in order to control power at a specific node in a wireless communication system employing a Frequency Division Duplex (FDD) scheme, a Transmit (Tx) signal of a transmitter is output at a maximum power when a receiver is in a weak electric field. As a result, the Tx signal output from the transmitter is introduced to the receiver in the same node, and thus operates as an interference signal with respect to a Receive (Rx) signal.
Various conventional methods are provided so as to reject the Tx signal introduced to the receiver. For example, as shown in FIG. 1, there is a conventional method in which an external Surface Acoustic Wave (SAW) filter 103 is inserted into a receiver 101 to reject the Tx signal. However, the method of using the SAW filter is inconvenient since the external element has to be additionally purchased.
A conventional method in which a receiver rejects a Tx signal introduced to a Low Noise Amplifier (LNA) 201 using a manual-type notch filter 203 is shown in FIG. 2A. That is, in a conventional receiver using the notch filter 203, a frequency band to be rejected is regulated by the notch filter 203 under the control of a Voltage ConTRol (VCTR) 205 in order to reject a signal in the frequency band. In this case, the LNA 201 and the notch filter 203 of the receiver are connected through a node A 211 and a node B 213, and detailed structures thereof are shown in FIG. 2B and FIG. 2C. The notch filter 203 is generally used to reject an image signal of an original signal. The Tx signal has conventionally been rejected by the use of the notch filter 203 according to a characteristic wherein a frequency difference between an Rx signal and a Tx signal is significantly large. The image signal simply has an effect on an actually received signal in a hetero-dyne structure, and has a significantly different frequency from the actually received signal since a frequency offset has an opposite feature according to a local oscillation signal in a reception band.
However, in the FDD-type wireless communication system, a Tx signal has a frequency band similar to that of an Rx signal. Therefore, there is a limit to the use of a method that rejects the Tx signal by the use of the notch filter. For example, in a Long Term Evolution (LTE) method, the Tx signal has a frequency band of 1900 Mhz and the Rx signal has a narrow frequency band of about 200 Mhz. Therefore, there is a limit when the Tx signal is rejected by using the manual-type notch filter as shown in FIGS. 2A to 2C.